Electrostatic Composition Based On A Polyamide Matrix

ABSTRACT

The invention relates to a composition based on a polyamide matrix comprising electrically conductive charges and antistatic agents. This composition makes it possible to obtain plastic articles, for example, body parts used in the automobile industry that are well-suited for painting by means of an electrostatic paint deposition process.

The present invention relates to a composition based on a polyamidematrix comprising electrically conductive fillers and antistatic agents.The forming of this composition makes it possible to obtain plasticarticles, such as, for example, bodywork components in the motor vehiclefield, having a good ability to be painted by a process for theelectrostatic deposition of the paint.

PRIOR ART

There exists a high demand in numerous industries for components made ofpolyamide materials. This is because these components are light and canbe conceived and designed more easily than components made of steel oraluminum, in particular in the field of the motor vehicle industry.

However, plastic components present problems when it is desired to paintthem.

Thus, for example, in the field of motor vehicles, there exist inparticular three main methods for painting electrostatically, that is tosay by movement of the particles under the influence of an electriccurrent. The first, referred to as “inline” process, refers to a processaccording to which the component made of plastic is assembled on thevehicle after the latter has been subjected to degreasing andelectroplating stages, followed by a drying stage. The component made ofplastic and the vehicle are subsequently painted and dried by heating.The second, referred to as “online” process, refers to a processaccording to which the component made of plastic is assembled on thevehicle at the beginning of the process mentioned above. The plasticcomponents are thus subjected to degreasing, electroplating and dryingstages at temperatures which can exceed 200° C. Consequently, for thistype of process, it is necessary for the components made of plastic tobe able to withstand higher temperatures. In a third process, referredto as “offline” process, the component made of plastic is first paintedin order to be subsequently assembled on the vehicle.

When processes for painting by electrostatic deposition are used, pooradhesion of the paint to conventional plastic components is obtained.Specifically, the paint easily comes away and does not adhere or onlyslightly adheres to the plastic components.

In order to render plastic components suitable for being painted by aprocess for the electrostatic deposition of the paint, it is known toadd conductive fillers to the thermoplastic matrix. However, theincorporation of these fillers has a negative effect on some propertiesof the plastics, such as the mechanical properties. Furthermore, theincorporation of conductive fillers significantly increases the meltviscosity of the thermoplastic matrices, rendering them unsuitable foruse in certain processes for the forming of these matrices.

Thus, there exists a need to manufacture and use plastic componentsexhibiting excellent mechanical properties, such as good impactstrength, and a good ability to be painted by a process for theelectrostatic deposition of the paint.

INVENTION

The Applicant Company has demonstrated a composition based on apolyamide matrix comprising electrically conductive fillers andantistatic agents.

This polyamide composition makes possible the forming of articlesexhibiting a good balance in mechanical properties, thermal propertiesand properties with regard to the ability to be painted, in particularby deposition of paint by an electrostatic process.

The plastic components according to the invention also exhibit asuitable linear thermal expansion coefficient (LTEC), in particular forthe field of the motor vehicle industry. The plastic componentsaccording to the invention furthermore have a good temperaturestability, a good surface appearance and a good propensity for molding.

These plastic components are thus very well suited to processes forpainting by electrostatic deposition, such as the “inline”, “online” and“offline” processes used in particular in the motor vehicle industry.

Moreover, it is apparent that the composition based on a polyamidematrix according to the invention has a significantly lower meltviscosity, in comparison with a polyamide composition comprising solelyconductive fillers, which is in particular advantageous for certainprocesses for the manufacture of components, such as injection molding.

DETAILED ACCOUNT OF THE INVENTION

A first subject matter of the present invention is a compositioncomprising at least one polyamide matrix:

at least 2% by weight of electrically conductive fillers; and

at least 1% by weight of antistatic agents; the percentages by weightbeing expressed with respect to the total weight of the composition.

This composition can comprise one or more types of electricallyconductive fillers and one or more types of antistatic agents.

Preferably, the composition according, to the invention is a compositionwhich dissipates static electricity and which exhibits a surfaceresistivity of between 10⁵ Ω and 10¹¹ Ω, according to Standard IEC61340-4-1.

The composition according to the present invention can also exhibit adischarge time of greater than or equal to 10 seconds, preferably ofgreater than or equal to 30 seconds, more preferably of greater than orequal to 50 seconds, measured according to Standard IEC 61340-5-1. Thedischarge time can, for example, be measured on a sheet (for examplehaving the following dimensions: 200×150×3 mm) obtained from thecomposition according to the invention, to which a charge of 1000 volts(V) is applied. The discharge time corresponds to the time necessary forthe electrical voltage at the surface of the sheet to change from 1000 Vto 100 V.

The parameters of surface resistivity and of discharge time of thecomposition of the invention are highly appropriate in particular forthe production of articles which are highly suitable for painting andwhich have a good compromise in mechanical properties.

The composition according to the invention can comprise from 2 to 50% byweight of electrically conductive fillers, with respect to the totalweight of the composition, preferably from 2 to 30% by weight, morepreferably still from 2 to 10% by weight, particularly from 2 to 5% byweight.

The electrically conductive fillers are preferably chosen from the groupconsisting of: a carbon black, a metal, a graphite, a conductivepolymer, a glass and/or an inorganic filler coated with a metal layer,and/or their mixture.

The glass and/or the inorganic fillers can be coated with a layer ofmetal, such as nickel, aluminum, silver, iron, chromium and/or titanium,for example.

The electrically conductive fillers can be in the form of spheres, suchas, for example, in the form of microspheres and/or nanospheres; oftubes, such as, for example, in the form of microtubes and/or nanotubes;and/or of fibers, such as, for example, in the form of microfibersand/or nanofibers. These fibers can be cut up and/or ground.

Use may be made, as conductive polymer, for example, of polyaniline,polypyrrole, polythiophene and/or poly-acetylene.

Preferably, the conductive filler according to the invention is carbonblack.

The conductive carbon black is described in particular in Carbon Black,Second Edition, Revised and Expanded, Science and Technology, edited byJ. B. Donnet, R. C. Bansal and M. J. Wang, Marcel Dekker Inc., pages271-275. Preferably, the composition according to the inventioncomprises from 2 to 10% by weight of carbon black, preferably from 2 to5% by weight, particularly from 2 to 4% by weight, as electricallyconductive fillers, with respect to the total weight of the composition.

The antistatic agents used according to the present invention can alsobe referred to as “dissipating electrostatic agents”.

Preferably, the composition according to the invention comprises from 1to 30% by weight of antistatic agents, with respect to the total weightof the composition, more preferably still from 5 to 20% by weight.

The antistatic agents can be chosen, for example, from the groupconsisting of polyetheramides, sodium alkyl-sulfonates,alkylbenzenesulfonates, primary, secondary or tertiary amines,ethoxylated amines, ethoxylated alcohols, glyceryl monostearates,distearates or tristearates, and their mixtures.

The term “polyetheramides” is understood to mean various types ofpolymers comprising one or more polyamide blocks and one or morepoly(alkylene oxide) blocks.

Preferably, the polyetheramide is a block polymer compound representedby the formula (I):

in which:

n is an integer between 5 and 50;

X represents an oxygen atom or an NH group;

PAO represents a poly(alkylene oxide) block;

PA represents a polyamide block, the repeat unit of which is representedby either of the formulae (IIa) or (IIb):

in which: R¹, R² and R³ are aromatic or aliphatic radicals comprising 4to 36 carbon atoms.

The block copolymer represented by the formula (I) is apolyether-block-amide or a polyetheresteramide. Such compounds are soldin particular by Atofina under the name of Pebax® and Ciba under thename of Irgastat. They comprise polyamide blocks and poly(alkyleneglycol) blocks. The number of blocks of each nature is between 3 and 50.It is preferably between 10 and 15. The number of blocks is representedby the integer n in the formula (I).

The polyamide blocks can be represented by either of the formulae (IIa)or (IIb) represented above. The blocks of formula (IIa) are polyamidesof the type of those obtained by polymerization starting from lactamsand/or amino acids. The processes for the polymerization of suchcompounds are known: mention is made, inter alia, of anionicpolymerization or melt polycondensation, for example in a VK tube. The(IIb) blocks are of the type of those obtained by polycondensation ofdicarboxylic acids with amines.

Preferably, X represents an oxygen atom, the formula (I) thus being asfollows:

According to the embodiment where the polyamide block is represented bythe formula (IIa), the radical R¹ is advantageously chosen from thefollowing radicals:

the linear divalent pentyl radical: the polyamide block is then apolyamide 6 block;

the unbranched divalent decyl radical (10 carbon atoms): the polyamideblock is then a polyamide 11 block;

the unbranched divalent undecyl radical (11 carbon atoms): the polyamideblock is then a polyamide 12 block.

According to the embodiment where the polyamide block is represented bythe formula (IIb), the pairs of radicals R² and R³ are advantageouslychosen from the following pairs:

R²=linear divalent butyl radical, R³=linear divalent hexyl radical:polyamide 6,6 block;

R²=linear divalent butyl radical, R³=linear divalent butyl radical:polyamide 4,6 block;

R²=linear divalent octyl radical, R³=linear divalent hexyl radical:polyamide 6,10 block.

The poly(alkylene oxide) block can be chosen from poly(ethylene oxide),poly(trimethylene oxide) or poly(tetramethylene oxide) blocks. In thecase where the block is based on poly(ethylene oxide), it can comprisepropylene glycol units at the ends of the block.

The average molecular weights of each of the blocks are independent ofone another. However, it is preferable for them to be close to oneanother. The average molecular weight of the PAO blocks is preferablybetween 1000 and 3000 g/mol. The average molecular weight of the PAblocks is advantageously between 1000 and 3000 g/mol.

The compound of formula (I) can be obtained by catalyzed reactionbetween polyamide macromolecular chains, the end functional groups ofwhich are carboxylic acid functional groups, and polyetherdiol chains,that is to say poly(alkylene oxide) macromolecular chains, the endfunctional groups of which are alcohol functional groups. They are, forexample, poly(ethylene glycol) chains comprising alcohol endings.

The reaction between the end functional groups of the blocks can becatalyzed by tetraalkyl orthotitanates or zirconyl acetate.

According to a specific embodiment of the invention, the modifyingcompounds of formula (I) have a melting point of greater than 150° C.,preferably of between 150 and 250° C.

The polyamide matrix according to the invention is generally composed ofat least one (co)polyamide chosen from the group consisting of:(co)polyamide 6; 4; 11; 12; 4,6; 6,6; 6,9; 6,10; 6,12; 6,18; 6,36; 6(T);9(T); 6(I); MXD6; their copolymers and/or blends.

Mention may be made, for example, of semicrystalline or amorphouspolyamides, such as aliphatic polyamides, semiaromatic polyamides andmore generally linear polyamides obtained by polycondensation between analiphatic or aromatic saturated diacid and an aromatic or aliphaticsaturated primary diamine, polyamides obtained by condensation of alactam or of an amino acid, or linear polyamides obtained bycondensation of a mixture of these various monomers. These copolyamidescan, for example, be poly(hexamethylene adipamide), the polyphthalamidesobtained from terephthalic and/or isophthalic acid, the copolyamidesobtained from caprolactam, and from one or more monomers generally usedfor the manufacture of polyamides, such as adipic acid, terephthalicacid and/or hexamethylenediamine.

Polyamide 6(T) is a polyamide obtained by polycondensation ofterephthalic acid and hexamethylenediamine. Polyamide 9(T) is apolyamide obtained by polycondensation of terephthalic acid and adiamine comprising 9 carbon atoms. Polyamide 6(I) is a polyamideobtained by polycondensation of isophthalic acid andhexamethylenediamine. Polyamide MXD6 is a polyamide obtained bypolycondensation of adipic acid and meta-xylylenediamine.

The composition can comprise one or more (co)polyamides obtained as ablend or as a copolymer, for example.

The polyamide matrix can in particular be a polyamide comprising star orH macromolecular chains and, if appropriate, linear macromolecularchains. The polymers comprising such star or H macromolecular chains aredisclosed, for example, in the documents FR 2 743 077, FR 2 779 730,U.S. Pat. No. 5,959,069, EP 0 632 703, EP 0 682 057 and EP 0 832 149.

According to another specific alternative form of the invention, thepolyamide matrix of the invention can be a polymer of random tree type,preferably a copolyamide exhibiting a random tree structure. Thesecopolyamides of random tree structure and the process for thepreparation thereof are disclosed in particular in document WO 99/03909.The thermoplastic matrix of the invention can also be a compositioncomprising a linear thermoplastic polymer and a star, H and/or treethermoplastic polymer as described above. The thermoplastic matrix ofthe invention can also comprise a hyperbranched copolyamide of the typeof those disclosed in the document WO 00/68298. The thermoplastic matrixof the invention can also comprise any combination of linear, star, H ortree thermoplastic polymer or hyperbranched copolyamide as describedabove.

According to a specific characteristic of the invention, the polyamidematrix of the composition is composed of a blend of a polyamide with oneor more other polymers, preferably of (co)polyamide type. A blend of(co)polyamide with at least one polymer chosen from the group consistingof: polyphenylene ether (PPE), poly(vinyl chloride) (PVC), theacrylonitrile-butadiene-styrene (ABS) polymer, polyethylene (PE),polypropylene (PP), poly(ethylene terephthalate) (PET) and/orpoly(butylene terephthalate) (PBT), can also be envisaged.

The polyamide composition according to the invention can comprisereinforcing and/or bulking fillers preferably chosen from the groupconsisting of fibrous fillers, such as glass fibers, metal fibers orcarbon fibers; inorganic fillers, such as clays, kaolin, wollastonite,mica, talc and glass beads; finely dispersible reinforcingnanoparticles, such as montmorillonite; or made of thermosettingmaterial. The level of incorporation of these fillers is in accordancewith the standards in the field of composite materials. The level offiller can, for example, be from 1 to 70% by weight, preferably from 10to 60% by weight, with respect to the total weight of the composition.

The polyamide composition according to the invention can also compriseat least one agent which modifies the impact strength chosen, forexample, from the group consisting of: ethylene-propylene (EP)optionally grafted with maleic anhydride, ethylene-propylene-diene(EPDM) terpolymer optionally grafted with maleic anhydride, elastomericcopolymers, such as styrene-maleic anhydride (SMA), for example,ultra-low-density polyethylene (ULDPE), linear low density polyethylene(LLDPE), styrene-butadiene (SBS and SBR) compounds,styrene-ethylene-butadiene-styrene (SEBS) compounds, polypropylene (PP),acrylic elastomers (such as polyacrylate elastomers), copolymers andterpolymers of ethylene with acrylic or methacrylic derivatives and/orwith vinyl acetate, ionomers, acrylonitrile-butadiene-styrene (ABS)terpolymer and acrylic-styrene-acrylonitrile (ASA) terpolymer. Themodifiers of the impact strength can optionally comprise grafted groups,such as maleic anhydride, for example. The modifiers of the impactstrength according to the invention can also be combinations, blends,homopolymers, copolymers and/or terpolymers of the compounds mentionedabove. The modifiers of the impact strength are chosen by a personskilled in the art for their compatibility with the polyamide matrix.

The polyamide composition according to the invention can additionallycomprise one or more additives commonly used by a person skilled in theart in thermoplastic compositions used in particular for the manufactureof molded articles. Mention may thus be made, as example of additives,of heat stabilizers, flame retardants, molding agents, such as calciumstearate, UV stabilizers, antioxidants, lubricants, abrasion reducers,pigments, dyes, plasticizers, laser marking promoters, waxes or agentswhich modify the impact strength. By way of examples, the antioxidantsand heat stabilizers are, for example, alkaline halides, copper halides,sterically hindered phenolic compounds, organic phosphites and aromaticamines.

The present invention also relates to a process for the preparation of apolyamide composition as defined above in which at least 2% by weight ofelectrically conductive fillers and at least 1% by weight of antistaticagents are blended with a polyamide matrix, optionally in the moltenstate.

The blending can be carried out in the molten state, for example in asingle- or twin-screw extruder, or by blending without conversion to themolten state, for example in a mechanical mixer. The compounds can beintroduced simultaneously or successively. Any means known to a personskilled in the art relating to the introduction of the various compoundsof a thermoplastic composition can be used. Use is generally made of anextrusion device in which the material is heated, subjected to a shearforce and conveyed. Such devices are fully known to a person skilled inthe art.

The composition according to the invention, when it is prepared using anextrusion device, can be put into the form of granules.

The electrically conductive fillers and antistatic agents can be blendedbeforehand, for example by continuous or batchwise mixing. To do this,use may be made, for example, of a Banbury mixer.

A concentrated blend, preferably based on polyamide, comprising theelectrically conductive fillers and/or the antistatic agents, forexample prepared according to the method described above, can also beadded to the polyamide matrix. This masterblend can, for example, beprepared by preblending the various compounds.

Thus, the present invention also relates to a process for thepreparation of a polyamide composition as described above in which atleast one polyamide matrix is blended with:

a concentrated blend based on a thermoplastic matrix comprising at least20% by weight of electrically conductive fillers, and

at least 1% by weight of antistatic agents.

The masterblend can comprise, for example, from 20 to 50% by weight ofelectrically conductive fillers, such as carbon black.

This masterblend is based on a thermoplastic matrix, for example chosenfrom the group consisting of: a (co)polyamide, an ethylene-vinyl acetate(EVA) copolymer, an ethylene-acrylic acid (EAA), a polyethylene (PE), apolypropylene (PP), their copolymers and/or blends.

It should be noted that the masterblend can also comprise antistaticagents according to the invention.

Numerous methods for blending the (co)polyamides of the invention withthe reinforcing and/or bulking fillers, agents which modify the impactstrength and/or additives can be envisaged. For example, these can beintroduced as a blend with the (co)polyamide in the molten state beforethe manufacture of granules. Some of these fillers, agents and/oradditives can also be added during the polymerization of the(co)polyamide.

The present invention also relates to a process for the manufacture ofan article by forming a composition according to the invention by aprocess chosen from the group consisting of an extrusion process, suchas the extrusion of thin sheets and films, a molding process, such ascompression molding, and an injection process, such as injectionmolding.

The articles according to the invention can, for example, be automobilecomponents, in particular bodywork components, pipes intended for thetransportation of liquids or gases, tanks, coverings, films and/orcovers made of plastic for tanks.

The present invention also relates to a process for the application ofpaint by electrostatic deposition on an article, characterized in thatan article of the invention as described above is used in this process.The paint can be applied to the article, for example, by spraying orimmersion. Generally, a process for the application of paint byelectrostatic deposition on an article comprises at least the followingstages: cataphoresis treatment of the article at temperatures of between150 and 250° C., application of a primer by electrostatic spraying andapplication of the paint by electrostatic spraying. Each spraying stagecan be followed by stage(s) of heating at temperatures of between 100and 200° C. and by stage(s) of cooling.

The present invention also relates to an article painted by a processfor the application of paint by electrostatic deposition.

Other details or advantages of the invention will become more clearlyapparent in the light of the examples given below solely by way ofindication.

Experimental Part

Materials Used:

PA 6,6: polyamide 6,6 with a relative viscosity of 2.7 (according toStandard ISO 307 using sulfuric acid as solvent) sold by RhodiaEngineering Plastics under the name Techny® 27 A00.

PA 6: polyamide 6 with a relative viscosity of 2.7 (according toStandard ISO 307 using sulfuric acid as solvent) sold by RhodiaEngineering Plastics under the name ASN 27 S.

Elastomer: EPR-g-MA: ethylene-propylene copolymer comprising graftedmaleic anhydride, with a density of 0.87 g/ml (measured according toASTM D792) and an MFR of 23 (measured according to ASTM D1238 at 280°C./2.16 kg).

Conductive carbon black: sold by Akzo under the name Ketjen Black 600®.

Polyetheramide: multisegmented block copolymer comprising 50% by weightof polyamide 6 blocks and 50% by weight of polyethylene glycol blocks, Xcorresponding to an oxygen atom, the average molecular weight of eachblock of which is approximately 1500 g/mol. Melting point: 204° C.according to Standard ASTM D3418.

Wollastonite: calcium silicate having a particle size of less than 10 μmand an aspect ratio of 5, surface treatment with a coupling agent.

Mica: mica of ground muscovite type having an average particle size,expressed as D₅₀, of less than or equal to 40 μm and a bulk density of450 g/l.

Others: corresponds to a blend of color stabilizer and of lubricants(calcium stearate).

Masterblend MB: blend based on EVA comprising 30% of conductive carbonblack Ketjen Black 300®, sold by Iridi Color Srl under the name MBUNNIRO N129.

EXAMPLE 1 Preparation of Compositions

Polyamide-based compositions are manufactured by blending variouscompounds mentioned below via a twin-screw extruder. The compositions,the compounds used and their amounts are given in table 1: TABLE 1Formulations A B C D E F G 1 2 PA 6,6 (%) 54.5 56.5 58.5 59.8 60.5 55.550.5 58.5 57.5 PA 6 (%) 10 10 10 10 0 0 0 0 0 Elastomer (%) 12 12 12 1212 12 12 12 12 Mica (%) 15 15 15 15 15 15 15 15 15 Others (%) 2.5 2.52.5 2.5 2.5 2.5 2.5 2.5 2.5 Polyetheramide (%) 0 0 0 0 10 15 20 10 10Carbon black (%) 6 4 2 1 0 0 0 2 3 Adhesion of the paint + + − − − −− + + Surface resistivity (Ω) n 5 × 10⁵ 7 × 10¹¹ insulator 25 × 10⁹ 25 ×10⁹ 25 × 10⁹ 16 × 10⁹ 5 × 10⁹ MFI (g/10 min) 0 0.1 5.1 8.5 14 15 17 1210 Notched Charpy impact 5.4 5.6 5.9 6.9 8.3 8.5 9 7.5 7 (kJ/m²)Elongation at break (%) 5.7 7.7 12.1 11.1 18 21 23 12.5 11 Tensilemodulus (N/mm²) 3540 3700 3530 3510 3210 3250 2910 3100 3210 HDT (° C.)200 201 206 208 205 202 192 205 205

The percentages of the various components are expressed by weight, withrespect to the total weight of the composition.

The properties are measured in the following way:

MFI (melt flow index), according to Standard ISO 1133 at 275° C. with aload of 5 kg.

Notched Charpy impact according to Standard ISO 179/1 eA at 23° C.

Elongation at break, according to Standard ISO 527 at 23° C.

Tensile modulus, according to Standard ISO 527 at 23° C.

HDT (heat deflection temperature), according to Standard ISO 75Be with aload of 0.45 N/mm².

Surface resistivity, according to Standard IEC 61340-4-1. Measurement iscarried out on an injection-molded sheet (200×150×3 mm) by placing theprobes of a device for measuring the resistance (Metriso 2000 ESD) at adistance of 1 cm from one another. A voltage of 100 volts is applied andthe surface resistivity of the sheet is measured. The measurement iscarried out in a room at a temperature of 23° C. approximately and arelative humidity of 50%.

Adhesion of the paint by electrostatic deposition: a sheet isinjection-molded from the above compositions. The paint is applied tothe sheets by an “online” process for painting by cataphoresis in sevenstages: stage 1: e-coat simulation (cataphoresis treatment) at 185° C.for 30 minutes. Stage 2: cooling for 20 minutes. Stage 3: application ofthe primer, BASF PMR82, by electrostatic spraying. Stage 4: heating at160° C. for 30 minutes. Stage 5: cooling for 20 minutes. Stage 6:application of a white paint by electrostatic spraying. Stage 7: coolingfor 20 minutes. Poor adhesion of the paint by electrostatic deposition(recorded as−in the above table) is recorded if an orangepeelappearance, a lack of paint and/or poor adhesion of the paint to thesheet are observed. In the contrary case, good adhesion of the paint(recorded as+in the above table) is observed.

In the above table, n means not measured.

EXAMPLE 2 Preparation of Compositions

Polyamide-based compositions are manufactured by blending variouscompounds mentioned below via a twin-screw extruder. The compositions,the compounds used and their amounts are given in table 2: TABLE 2Formulations 3 4 PA 6,6 (%) 46.95 43.95 Elastomer (%) 7 7 Wollastonite(%) 26 26 Others (%) 2.05 2.05 Polyetheramide (%) 11 10 Masterblend MB(%) 7 11 Adhesion of the paint + + Surface resistivity (Ω) 45 × 10⁹ 3 ×10⁹ MFI (g/10 min) 23.5 18.7 Notched Charpy impact (kJ/m²) 9.2 8Elongation at break (%) 12.8 10.8 Tensile modulus (N/mm²) 2730 2570 HDT(° C.) 206 206

The percentages of the various components are expressed by weight, withrespect to the total weight of the composition.

1-19. (canceled)
 20. A composition comprising a polyamide matrix,comprising: at least 2% by weight of electrically conductive fillers;and at least 1% by weight of antistatic agents; the percentages byweight being expressed with respect to the total weight of thecomposition.
 21. The composition as claimed in claim 20, exhibiting asurface resistivity of between 10⁵ Ω and 10¹¹ Ω, measured according toStandard IEC 61340-4-1.
 22. The composition as claimed in claim 20,having a discharge time of greater than or equal to 10 seconds, measuredaccording to Standard IEC 61340-5-1.
 23. The composition as claimed inclaim 20, having from 2 to 50% by weight of electrically conductivefillers, with respect to the total weight of the composition.
 24. Thecomposition as claimed in claim 20, wherein the electrically conductivefillers are a carbon black, a metal, a graphite, a conductive polymer, aglass or an inorganic filler coated with a metal layer.
 25. Thecomposition as claimed in claim 20, having from 2 to 10% by weight ofcarbon black as electrically conductive fillers, with respect to thetotal weight of the composition.
 26. The composition as claimed in claim20, having from 1 to 30% by weight of antistatic agents, with respect tothe total weight of the composition.
 27. The composition as claimed inclaim 20, wherein the antistatic agents are a polyetheramide, a sodiumalkylsulfonate, an alkylbenzenesulfonate, primary, secondary or tertiaryamines, an ethoxylated amine, an ethoxylated alcohol, glycerylmonostearates, distearates or tristearates.
 28. The composition asclaimed in claim 20, wherein the antistatic agent is a polyetheramiderepresented by the formula (I):

in which: n is an integer between 5 and 50; X represents an oxygen atomor an NH group; PAO represents a poly(alkylene oxide) block; PArepresents a polyamide block, the repeat unit of which is represented byeither of the formulae (IIa) or (IIb):

in which: R¹, R² and R³ are aromatic or aliphatic radicals having 4 to36 carbon atoms.
 29. The composition as claimed in claim 28, wherein theradical R¹ is a linear divalent pentyl radical.
 30. The composition asclaimed in claim 28, wherein the PAO block is a poly(ethylene oxide)block.
 31. The composition as claimed in claim 20, wherein the polyamidematrix is composed of at least one (co)polyamide which is: (co)polyamide6; 4; 11; 12; 4,6; 6,6; 6,9; 6,10; 6,12; 6,18; 6,36; 6(T); 9(T); 6(I);MXD6; their copolymers or their blends.
 32. The composition as claimedin claim 20, wherein the composition further comprises at least onemodifier of the impact strength chosen from the group consisting of:ethylene-propylene (EP) optionally grafted with maleic anhydride,ethylene-propylene-diene (EPDM) terpolymer optionally grafted withmaleic anhydride, styrene-maleic anhydride (SMA), ultra-low-densitypolyethylene (ULDPE), linear low density polyethylene (LLDPE),styrene-butadiene (SBS and SBR) compounds,styrene-ethylene-butadiene-styrene (SEBS) compounds, polypropylene (PP),acrylic elastomers, copolymers and terpolymers of ethylene with acrylicor methacrylic derivatives and/or with vinyl acetate, ionomers,acrylonitrile-butadiene-styrene (ABS) terpolymer andacrylic-styrene-acrylonitrile (ASA) terpolymer.
 33. A process for thepreparation of a polyamide composition as claimed in claim 20,comprising the step of blending at least 2% by weight of electricallyconductive fillers and at least 1% by weight of antistatic agents with apolyamide matrix, optionally in the molten state.
 34. A process for thepreparation of a polyamide composition as claimed in claim 20,comprising the step of blending the polyamide matrix with: aconcentrated blend based on a thermoplastic matrix comprising at least20% by weight of electrically conductive fillers, and at least 1% byweight of antistatic agents.
 35. The process as claimed in claim 34,wherein the thermoplastic matrix is chosen from the group consisting of:the (co)polyamide, ethylene-vinyl acetate (EVA) copolymer,ethylene-acrylic acid (EAA), polyethylene (PE), polypropylene (PP),their copolymers and their blends.
 36. A process for the manufacture ofan article by forming a composition as claimed in claim 20 by anextrusion process, a molding process or an injection process.
 37. Anarticle obtained by forming a composition as claimed in claim
 20. 38.The article as claimed in claim 37, painted by a process of applying apaint by electrostatic deposition.